Multi-color rotary offset printing machines are known; customarily, each color of ink is applied by a separate blanket cylinder on the substrate. Such machines, which are customary and standard in the printing field, have the disadvantage that a plurality of impression lines are needed for applying the ink of any one color to paper. Since offset rotary printing machines apply not only ink but also conduct damping liquid, typically water, to the substrate, typically paper, the paper is mechanically stressed since it becomes wetted by the damping liquid and then is passed through a plurality of printing lines where it is subjected to kneading. Such mechanical stressing of paper, particularly when the paper is of poor quality, leads to difficulties with respect to registration, which increases adjustment time of the machine and rejects. As the quality of paper decreases, each printing line, additionally, causes slight tearing or removal of paper particles from the paper substrate, leading to fuzzy printing and rapid soiling of the machine, requiring increased maintenance and cleaning thereof.
It has previously been proposed--see U.S. Pat. No. 2,894,452 and German Pat. No. 442,934--to provide a machine in which two differently colored inks can be printed simultaneously. Two plate cylinders are applied to a common blanket cylinder which then effects printing therefrom. Such arrangements have the disadvantage that set-up requires a long time, and for a substantial period it is not possible to obtain clear, sharp impression or printing. The disadvantage can be ameliorated to some extent by associating with each plate cylinder two dampers--see German Pat. No. 2,323,871, which, however, has the disadvantage that utilizing two dampers for each plate cylinder substantially increases the mechanical complexity of the printing machine, and introduces problems of accessibility to the respective components of the printing machine system. Additionally, the adjustment of the quantity of damping liquid applied by the respective dampers, and maintenance of relative adjustment of the two dampers with respect to each other, is complex and requires supervision.
It has also been proposed to provide an offset printing machine which can be used, selectively, for multi-color prime printing or prime and verso printing--see German Pat. No. 271,645. This printing machine utilizes a central printing or impression cylinder which is surrounded by a plurality of partial printing stations, each having a blanket cylinder, a plate cylinder, and associated dampers and inkers. Such a machine applies ink on the rubber blanket of the impression cylinder, for example from two partial printing systems, if prime and verso printing is to be carried out. The color inks are then printed simultaneously on the substrate. This arrangement, in order to apply two colors, requires three blanket cylinders. Both, when applying prime, as well as prime and verso printing, each one of the prime printing inks is applied by a blanket cylinder on the substrate, which cooperates with the common impression or printing cylinder. Consequently, problems with respect to registration cannot be excluded. The arrangement further presupposes that the partial printing systems are located about or around the central impression cylinder, which, in systems having a plurality of components, may lead to problems of accessibility. Such a machine cannot be readily expanded for different types of printing, for example in modular fashion, and the versatility thereof, therefore, is lessened.